US9200355B2ActiveUtilityPatentIndex 80
Process for manufacturing iron-carbon-manganese austenitic steel sheet with excellent resistance to delayed cracking, and sheet thus produced
Est. expiryJul 11, 2026(expired)· nominal 20-yr term from priority
C21D 8/02C21D 1/42C21D 1/26C23C 2/06C21D 6/001C22C 38/02C21D 6/008C22C 38/08C22C 38/12C21D 1/767Y10T428/12799C23C 28/025C21D 9/46C23C 28/028C22C 38/001C23C 28/021C23C 28/023C21D 8/0236C22C 38/04C22C 38/002B32B 15/013C22C 38/06C22C 38/16C21D 6/004C21D 6/005C23C 2/02C23C 2/28C23C 30/00Y02P10/25
80
PatentIndex Score
10
Cited by
19
References
32
Claims
Abstract
An austenitic steel sheet excellent in resistance to delayed cracking, the composition of said steel comprising, in weight: 0,35%<C<1,05%, 15%<Mn<26%, Si<3%, Al<0,050%, S<0,030%, P<0,080%, N<0,1%, at least one metallic element X chosen among vanadium, titanium, niobium, molybdenum, chromium: 0,050%<V<0,50%, 0,040%≦Ti<0,50%, 0,070%<Nb<0,50%, 0,14%<Mo<2%, 0,070%<Cr<2% and optionally, one or several elements chosen among 0,0005%<B<0,010%, Ni<2%, Cu<5%, the remainder being iron and unavoidable impurities inherent to fabrication, including hydrogen, the quantity Xp of said at least one metallic element under the form of carbides, nitrides or carbonitrides being, in weight: 0,030%<VP<0,40%, 0,030%<Tip<0,50%, 0,040%<Nbp<0,40%, 0,14%<Mop<0,44%, 0,070%<Crp<0,6%, the hydrogen content Hmax designating the maximal hydrogen content that can be measured from a series of at least five specimens, and the quantity Xp, in weight, being such that (I) <3,3. 1000 H max X p ( I )
Claims
exact text as granted — not AI-modifiedThe invention claimed is:
1. A process of fabricating a steel sheet, comprising:
(A) casting a steel with composition, comprising Fe, hydrogen, and, by weight:
0.35%≦C≦1.05%;
15%≦Mn≦26%;
Si≦3%;
Al≦0.050%;
S≦0.030%;
P≦0.080%;
N≦0.1%;
at least one metallic element X selected from the group consisting of vanadium, titanium, niobium, molybdenum, and chromium, in a percentage as follows
0.050%≦V≦0.50%,
0.040%≦Ti≦0.50%,
0.070%≦Nb≦0.50%,
0.14%≦Mo≦2%; and
0.070%≦Cr≦2%;
to obtain a semi-product and heat-treating the semi-product at a temperature between 900 and 1000° C. for a time between 5 and 20 days;
(B) additional reheating the semi-product to a temperature between 1100° C. and 1300° C.;
(C) hot rolling the semi-product up to an-end-of-rolling temperature to obtain a sheet;
(D) directly after the hot rolling (C), coiling the sheet; and
(F) after the coiling (D), performing at least one soaking treatment where the sheet is soaked at a temperature Θ comprised between 250 and 900° C. during a time t of at least 15 s so as to obtain a hydrogen content H max after soaking, H max designating a maximal hydrogen content that can be measured from a series of at least five specimens, and a quantity X p , in weight, satisfies:
1000
H
max
X
p
≤
3.3
wherein a reheating temperature, the end-of-rolling temperature, a coiling temperature, and an annealing temperature are chosen to obtain the following quantity X p of metallic element in the form of carbides, nitrides, or carbonitrides:
0.030%≦V p ≦0.40%
0.030%≦Ti p ≦0.50%
0.040%≦Nb p ≦0.40%
0.14%≦Mo p ≦0.44%
0.070%≦Cr p ≦0.6%.
2. The process of claim 1 , wherein the temperature Θ and time t are chosen such that
1000
H
max
X
p
≤
2.5
.
3. The process of claim 1 , further comprising:
soaking the steel sheet; and
wherein a quantity X p of the at least one metallic element X in the form of carbides, nitrides, or carbonitrides, is, by weight:
0.030%≦V p ≦0.40%;
0.030%≦Ti p ≦0.50%;
0.040%≦Nb p ≦0.40%;
0.14%≦Mo p ≦0.44%;
0.070%≦Cr p ≦0.6%,
under a pure nitrogen or argon atmosphere with a dew point lower than −30° C. at a temperature Θ between 250 and 900° C., with a dynamic circulation of a regenerated atmosphere.
4. The process of claim 3 , wherein the steel sheet comprises a Zn or Zn—Y alloy coating,
wherein element Y is at least one selected from the group consisting of Ni, Cr, and Mg, but not Fe or Mn,
wherein the temperature and time of the soaking satisfy Θ(° C.)Ln(t(s))≧2200.
5. A process of fabricating a hot rolled coated steel sheet, comprising:
(A) casting a steel with a composition comprising Fe, and, by weight:
0.35%≦C≦1.05%;
15%≦Mn≦26%;
Si≦3%;
Al≦0.050%;
S≦0.030%;
P≦0.080%;
N≦0.1%;
at least one metallic element X selected from the group consisting of vanadium, titanium, niobium, molybdenum, and chromium, in a percentage as follows
0.050%≦V≦0.50%,
0.040%≦Ti≦0.50%,
0.070%≦Nb≦0.50%,
0.14%≦Mo≦2%
0.070%≦Cr≦2%; and
to obtain a semi product and heat-treating the semi-product at a temperature between 900 and 1000° C. for a time between 5 and 20 days;
(B) additionally heating the semi product to a temperature between 1100 and 1300° C.;
(C) hot rolling the semi-product with an end-of-rolling temperature of 890° C. or higher to obtain a sheet;
(D) directly after the hot rolling (C), coiling the sheet at a temperature below 580° C.;
(G) coating the sheet with a Zn or Zn—Y alloy coating to obtain a coated sheet;
(H) performing at least one soaking treatment on the coated sheet under a pure nitrogen or argon atmosphere with a dew point lower than −30° C., at a temperature Θ between 250 and 900° C. during a time t, said temperature and time satisfying: Θ(° C.)Ln(t(s))≧2200.
6. The process of claim 5 , further comprising, between the coiling (D) and the coating (G):
(E) performing at least one cold rolling on the sheet; and
(F) performing at least one annealing treatment on the sheet, wherein the annealing treatment comprises a heating rate V h of between 2 and 10° C./s, at a temperature T s of between 700 and 870° C. for a time between 30 and 180 s and a cooling rate of between 10 and 50° C./s.
7. The process of claim 4 or 5 , wherein Θ(° C.)Ln(t(s))≧2450.
8. The process of claim 4 or 5 , wherein Θ(° C.)Ln(t(s))≧2750.
9. The process of claim 3 or 5 , wherein soaking temperature Θ is below recrystallization temperature.
10. The process of claim 1 , 3 , or 5 , wherein the soaking is performed by continuous annealing.
11. The process of claim 1 , 3 , or 5 , wherein the soaking is performed by batch annealing.
12. The process of claim 11 , wherein the soaking is performed by open coil annealing.
13. The process of claim 1 , 3 , or 5 , wherein the soaking is performed by induction heating.
14. The process of claim 13 , wherein the soaking is performed with a transversal electromagnetic field.
15. The process of claim 1 , 3 , or 5 , wherein the steel sheet is cold formed to obtain a part, and the soaking is performed before or after cold forming of the part.
16. The process of claim 1 , 3 , or 5 , wherein the steel comprises:
0.70%≦C≦1.05%.
17. The process of claim 1 , 3 , or 5 , wherein the steel comprises:
0.35%≦C≦0.50%.
18. The process of claim 1 , further comprising:
(E) after the coiling, cold rolling and annealing the sheet, wherein the soaking treatment (F) is performed after the cold rolling and annealing (E).
19. The process of claim 1 , wherein the steel comprises boron.
20. The process of claim 3 , wherein the steel comprises boron.
21. The process of claim 5 , wherein the steel comprises boron.
22. The process of claim 3 , wherein the steel comprises hydrogen and the sheet has a hydrogen content, H max , designating the maximal hydrogen content that can be measured from a series of at least five specimens, and the quantity, X p , by weight, such that:
1000
H
max
X
p
<
3.3
.
23. The process of claim 3 , wherein the steel comprises hydrogen and the sheet has a hydrogen content, H max , designating the maximal hydrogen content that can be measured from a series of at least five specimens, and the quantity, X p , by weight, such that
1000
H
max
X
p
≤
2.5
.
24. The process of claim 5 , wherein the soaking treatment (H) is performed after the coating (G).
25. The process of claim 1 , wherein
1000
H
max
X
p
<
3.3
.
26. The process of claim 5 , wherein the steel comprises hydrogen and the sheet has a hydrogen content, H max , designating the maximal hydrogen content that can be measured from a series of at least five specimens, and the quantity, X p , by weight, such that:
1000
H
max
X
p
<
3.3
.
27. The process of claim 5 , wherein the steel comprises hydrogen and the sheet has a hydrogen content, H max , designating the maximal hydrogen content that can be measured from a series of at least five specimens, and the quantity, X p , by weight, such that
1000
H
max
X
p
≤
2.5
.
28. The process of claim 22 , wherein
2.5
≤
1000
H
max
X
p
≤
3.3
.
29. The process of claim 26 , wherein
2.5
≤
1000
H
max
X
p
≤
3.3
.
30. The process of claim 1 , further comprising, at least one element selected from the group consisting of boron, nickel, and copper, in a percentage as follows
0.0005%≦B≦0.010%,
Ni≦2%, and
Cu≦5%.
31. The process of claim 3 , further comprising, at least one element selected from the group consisting of boron, nickel, and copper, in a percentage as follows
0.0005%≦B≦0.010%,
Ni≦2%, and
Cu≦5%.
32. The process of claim 5 , further comprising, at least one element selected from the group consisting of boron, nickel, and copper, in a percentage as follows
0.0005%≦B≦0.010%,
Ni≦2%, and
Cu≦5%.Cited by (0)
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